Paper Wasps, Yellowjackets and Solitary Wasps

E-239
7-03
Paper Wasps, Yellowjackets
and Solitary Wasps
Glen C. Moore and Mike E. Merchant*
S
everal kinds of stinging wasps can pose serious health and safety threats to humans.
Most problems occur when people are stung
after getting too close to wasp nests constructed
near homes, buildings and recreational areas. In
such situations, it may be necessary to control
the wasps, even though most wasps are beneficial pollinators and predators of other insects.
Although thousands of North American wasp
species can “sting,” few are potentially dangerous to
humans. Of the fewer than 40 species of stinging
(vespid) wasps that occur in the United States, only a
handful are important stinging pests in Texas. This
publication reviews the most important and common
species likely to be found around the home.
Kinds of Wasps
All wasps, bees and ants belong to the scientific
order called Hymenoptera. The Hymenoptera comprise some of the most interesting and important
insects, including many species that are beneficial
predators and parasites of pest insects, and many useful pollinator species. Besides ants and bees, the most
important stinging Hymenoptera belong to the wasp
family Vespidae.
Most vespid wasps are social insects, living in nests
that they build and defend cooperatively. The stinger
of social wasps is primarily a defensive tool, designed
to protect both nest and colony. However, when
defending a colony, multiple wasp stings can occur
quickly, with each wasp stinging one or more times.
Vespid wasp nests are constructed of a paper-like
material and may be found either
above or below ground.
Another important group of wasps
with stingers are the solitary wasps.
The stinger of solitary wasps is used
primarily for subduing prey. Although
solitary wasps may be common and
are often thought dangerous by people who fear wasps, solitary wasps
rarely sting humans. Most are entirely beneficial, feeding on spiders,
crickets, cicadas and caterpillars.
Knowing how to distinguish between
solitary and social wasps can be useful in determining whether control is
justified.
Wasp Stings
Paper Wasp (Polistes exclamans) on nest.
(Photo – Garland McIlveen)
Wasps sting their victims and
inject venom from the rear of the
abdomen (tail). The stinger in all
*Extension Agent, IPM and Associate Professor and Extension Entomologist; Texas Cooperative Extension
wasps do not leave a stinger in the skin and may sting
repeatedly.
Solitary wasps, on the other hand, rarely sting
unless mishandled or trapped against the skin. The
venom of solitary wasps is different from that of
social wasps and seldom causes more than momentary pain. Because solitary wasps do not build a community nest, they do not attempt to defend their nest.
wasps and bees is a modified egg-laying organ
(ovipositor); hence only females can sting.
Venom from ant, bee and wasp stings is responsible for 40 to 100 deaths per year in the United States.
Social wasp and bee venom contains more than 30
compounds, including biogenic amines, protein toxins
and various enzymes. Most deaths from insect stings
are the result of allergic reactions to venom proteins
and enzymes.
Wasp stings typically result in intense pain, with
swelling and redness at the site of the sting. Stings
around the head, eyes and neck are especially serious.
While pain is usually localized at the site of the sting,
large local and systemic (allergic) reactions are also
possible. Large local reactions occur when swelling
and pain extends beyond two inches from the site of
the sting. Swelling may involve an entire extremity,
such as a hand, arm or leg. Large local reactions are
usually not life-threatening, but may last for two to
seven days. About 5 percent of people who experience a large local reaction will suffer an anaphylactic
(serious systemic hypersensitivity) reaction if they are
stung subsequently.
Systemic allergic reactions occur when symptoms
are produced in body sites other than at the site of
the sting. These reactions — anaphylaxis or anaphylactic reactions — range from a widespread rash,
swelling and itching to difficulty breathing. In severe
reactions, victims may develop a rapid pulse and low
blood pressure, shock or respiratory distress and even
death. Respiratory conditions account for more than
half of all deaths due to Hymenoptera stings.
Anaphylaxis typically occurs within 20 to 30 minutes of a sting, although shock and death can occur as
quickly as 10 to 15 minutes. It is critical to get someone experiencing a systemic reaction to emergency
care immediately. If you know that you are allergic to
bee or wasp venom, consult your physician to see
whether you should carry an epinephrine emergency
kit or self-administer an antihistamine for life-saving
purposes.
Social Wasps
Paper Wasps
Paper wasps are one of the most common vespid
wasps seen around homes and buildings. They are 3/4
to 1 inch long and generally reddish-orange to dark
brown. They often have yellow body markings. Paper
wasps have three castes — infertile female workers,
which make up most of the wasps on nests during the
summer; males; and queens. Males and new queens
are produced primarily in late summer and fall.
Unlike yellowjackets and hornets, the paper wasp
queen is not much larger than the worker wasps.
Paper wasps build their nests from chewed wood
fibers. The comb, which hangs from a single filament,
is usually oriented downward and consists of a single
tier of hexagonal-shaped cells. Nests are most frequently seen under the eaves of houses but may also
be found in attics, garages, storage sheds, barns, on
shrubbery, trees and a variety of protected sites. The
typical mature paper wasp nest contains 20 to 30
adults and rarely more than 200 cells.
Life cycle. Colonies are founded in the spring by
queens that spend the winter in sheltered hiding
places. Although early season queens may cooperate
in founding a nest, by midsummer there is usually
only one active egg-laying queen per nest. New nests
are constructed every year, often in the same general
location where nests were built the previous season.
When Do Wasps Sting?
Vespid wasps are most likely to sting when their
nest is disturbed. All social wasps will vigorously
defend their nests when disturbed. These wasps
rarely sting away from the nest, unless trapped or
pressed against the skin.
Wasps and bees are instinctively attracted to the
upper bodies of animals, so in the event of an attack
it is best to cover your head and run away quickly.
The best defense is to run to a building, car or other
protected place. Victims who stand in place and
attempt to swat their attackers will continue to
receive stings as the wasps summon reinforcements
via chemical communication. Unlike honey bees,
Paper wasp (Polistes carolina) foundresses. When a wasp colony has more
than one foundress the size of the nest increases rapidly. However, only one
foundress becomes the queen.
(Photo – Garland McIlveen)
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Queen paper wasps lay a single egg per nest cell.
The newly hatched paper wasp larva is white and legless. As it grows in size, it fills the nest cell. The
queen, and later the workers, bring food to the larva.
Eventually, the larva matures, the cell is closed and
pupation occurs. After pupation, the adult wasp
emerges by chewing through the paper cell cover.
During late summer and fall, males and queen
paper wasps are produced. Males and females mate in
the fall. The males then die, and fertilized queens
enter sheltered locations for hibernation.
Overwintering paper wasp queens may join together, sometimes in large groups. They seem to prefer
high structures, such as the peaked attics of houses,
chimneys and tall buildings. During the winter, they
frequently enter homes and offices, especially during
warmer periods. Overwintering paper wasps are not
aggressive and may be captured and released outdoors or killed with a fly swatter.
Control. Aerial nests of paper wasps can easily be
eliminated using rapid knock-down insecticides or
aerosol products specifically designed for this purpose. Wasp sprays frequently contain the insecticides
pyrethrins, resmethrin, tetramethrin, bifenthrin,
cyfluthrin, lambda-cyhalothrin or permethrin.
Products containing carbaryl, acephate and dichlorvos
are also available for treating wasp colonies. Some
aerosol containers will propel the insecticide 10 to 40
feet or more.
For best results, treat in the late evening when
most wasps have returned to the nest. When spraying, stand well away from the colony and soak the
nest thoroughly. Do not remove the nest until all the
wasps are dead, which may require up to 2 days.
Then the nest should be removed and discarded.
voids of buildings, in open garages and storage sheds,
on porches, in abandoned furniture and in other
places that provide protection and are close to food
and water. Because of their scavenging behavior, yellowjackets are a menace around parks, camps and
suburban sites where people leave open food and discard garbage.
Yellowjacket workers forage to feed their larvae
insects and spiders. They also gather nectar, honeydew and other carbohydrates, but they do not store
honey as do bees.
Colony founding. Yellowjacket queens overwinter
under loose bark, in cracks and crevices and occasionally in attics or similar sheltered locations. They
emerge during the early spring and build small paper
nests in which they lay eggs. When the eggs hatch,
the queens feed the young larvae for about 18 to 20
days. After the first brood of workers emerge, the nest
may rapidly expand up to a foot long or larger within
a few days or weeks. Maximum colony size is
attained by August or September. This is followed by
the emergence of males and next year’s queens in
October and November. After mating, the males die
and inseminated queens usually seek sheltered places
to overwinter, abandoning the nest. Abandoned nests
rapidly decompose and are not reused the next year.
Occasionally, in sheltered sites or during mild winters, the nest may not be abandoned. In such cases,
so-called perennial colonies may be maintained by
both queen(s) and workers into the following year.
Perennial colonies are generally larger than annual
colonies.
Control. If not too close to areas of human activity,
yellowjacket nests should be left alone and the area
marked with a warning sign. In late fall or early winter, after the first
hard frost, most
yellowjacket nests
die; abandoned
nests can be
plugged up (with
or without treatment) to prevent
further infestations next year.
Yellowjackets
Yellowjackets are easily recognized but are often
confused with paper wasps. Baldfaced hornets are
also a type of yellowjacket wasp, but because of some
behavioral differences, they will be discussed separately.
Worker yellowjackets construct their nests of a
paper-like material consisting of wood fiber. Unlike
paper wasp nests, they are completely enclosed in an
envelope except for the entrance hole. In Texas, southern yellowjacket nest size may vary
from a few inches to 6 feet or larger,
and nests may contain up to 45 levels
of combs and 20,000 adult workers.
Yellowjackets are primarily ground
nesters, but they also construct aerial
nests. Subterranean nests may be
found in gardens, flower beds, pastures, roadside embankments and elsewhere. Aerial nests are typically constructed in trees, under eaves, in wall
Yellowjacket nest and yellowjacket workers (Vespuls squamosa) at entrance
hole.
(Photo – Garland McIlveen)
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Wasp control is dangerous and should not be
undertaken by anyone with a heart condition or
known allergies to bee or wasp venom. If you have
any doubt about your ability to safely control a wasp
nest, call a professional.
Underground yellowjacket wasp nests are best
treated with an insecticide dust. Dusts have the
advantage that they can be tracked deep into the nest
by wasps as they enter and exit. Crank or power-type
dusters can be used to blow dust into a wasp nest
entrance. A hose or plastic tube can be used to extend
the reach of the duster into otherwise inaccessible
nest entrances. Effective dusts include those containing carbaryl, esfenvalerate and permethrin. Be sure
the products have a label that allows their use on
insect nests in the soil. Use of acephate dusts under
or around homes should be avoided because of the
potential for indoor odor problems.
Aerosol sprays can also be used but may have a
lower success rate unless sufficient aerosol can be
injected directly into the nest entrance. Liquid insecticides applied as a spray are generally less effective on
subterranean nests, as they often soak into soil and
may not reach the nest in a sufficient quantity to
eliminate a colony.
Garbage cans can be attractive to foraging yellowjacket wasps at certain times of year. At such times, it
is especially important to ensure that all garbage
receptacles are closed tightly when not in use and
emptied daily. Yellowjacket wasp traps are commercially available and may help to reduce foraging numbers somewhat when properly maintained. However,
these devices do not effectively control wasp colonies.
Hornet nests almost always are above ground,
often high in trees. Occasionally, they may be
attached to the eaves of buildings. A mature colony
may contain 200 to 400 adults.
While the stings of hornets can be intensely
painful, hornets are less likely to attack than paper
wasps or yellowjacket wasps. Hornets typically nest
high in trees or in other remote locations, where they
pose no threat to humans and should be left undisturbed. When control is needed, apply a liquid insecticide from a safe distance of at least 10 to 15 feet.
Control products that include a refrigerant agent are
often used to quickly immobilize stinging insects.
Most residual insecticides such as permethrin,
cyfluthrin, bifenthrin, esfenvalerate, tetramethrin,
acephate and carbaryl will control hornet nests.
Pressurized aerosols designed for wasp control, pin
stream sprays from a good garden sprayer or spray
streams from a hose-end sprayer should be directed
toward the nest entrance and the nest thoroughly
soaked with spray.
Insecticide products containing synergized
pyrethrins and a rapidly volatilizing organic solvent,
such as Wasp Freeze, can be extremely useful. Treatment should be directed into the opening of the nest.
Hornet nests high in trees or in other remote locations where they pose no threat to humans should be
left unharmed. When attempting to control baldfaced
hornets, always wear protective clothing, such as a
bee suit, or hire a professional pest control operator.
Solitary Wasps
Cicada Killers
Horn ets
This large insect is 11/2 inches long, rusty red on
the head, thorax and wings and striped with black
The term hornet is often used in a general sense to
and yellow on the abdomen. These wasps may be
describe many kinds of wasps and yellowjackets.
considered a nuisance in landscapes during times of
Actually, the baldfaced hornet, Dolichovespula macuthe year when cicadas are present in shade trees.
lata, is the only “hornet” reported in Texas. Hornets
Cicada killer wasps appear formidable because of
construct a round or pear-shaped paper
their size and behavior. Male cicada
nest, up to 3 feet long. The grayish to
killers cannot sting but will buzz very
brown nest has two to four horizontally
near humans. Females will not sting
arranged combs inside and an entrance
unless handled but sometimes painfully
hole near the bottom.
sting people who are working on lawns
or step on their nests barefooted. Female
cicada killers dig galleries in lawns, gardens or flower beds, where they lay eggs
and provision the young larvae with paraBaldfaced hornet
lyzed cicadas. This nesting activity may
(Dolichovespula maculata)
damage lawns or vegetable gardens.
and nest on side of house.
Control is rarely warranted for this other(Photo – Garland McIlveen)
wise beneficial insect. When control is
necessary, sprinkle about 1 tablespoon of carbaryl
dust into the gallery hole and tamp the entrance shut.
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Cicada killer wasp (Sphecius speciosus).
Cricket-hunter wasps are seen most commonly
indoors during warm weather spells in the winter or
early spring. Infestations can be persistent and annoying. Though not normally aggressive, they can sting if
provoked.
The best solution is prevention. Fill any holes or
cracks in soil that might lead under the home. Seal
openings, such as weep holes, that might provide
access to wall voids. Ventilation weep holes should be
screened rather than caulked. Other cracks and gaps
in walls should be sealed with expanding foam, mortar or other appropriate material. In severe cases, wall
voids may be treated with pesticide aerosols or dusts;
however, there is little evidence that this treatment
works consistently. Adult wasps can be safely killed
with a fly swatter or captured and released outdoors.
(Photo – Mike E. Merchant)
Cricket Hunter Wasps
Mud Daubers
Cricket hunter wasps in the genus Liris are occasional indoor pests in Texas. These solitary wasps are
1/2 - 5/8 inches long and dull black with dusky-colored
wings. They spend much of their time searching for
crickets, which they attempt to sting, capture and
transport live to an underground hole. After a cricket
has been collected, the female lays a single egg on the
victim. The larva that hatches eventually develops
into an adult wasp.
Little is known about these insects. In urban areas,
cricket-hunter wasps may nest under or in the walls
of buildings. When this happens, the offspring of
nest-building females may emerge into indoor rooms.
Because numerous crickets may be provisioned within a wall void as described above, few or many wasps
may emerge indoors. In one case, more than 100
wasps were counted from a single bathroom, apparently emerging from a slab opening under a bathtub.
Liris wasp.
These wasps build small, tube-like nests of mud
under eaves, in attics and under the roofs of storage
buildings. Adult mud daubers are 3/4 to 1 inch long
and vary from dull black with bright yellow markings
to blackish or iridescent blue-black. They have longer,
more slender waists than most other wasps. As they
develop in the mud tubes, young larvae are generally
fed spiders, including the poisonous brown recluse.
Control. Since females do not defend their nests,
mud daubers structures can simply be removed by
hand with a
putty knife.
Mud daubers
can also be controlled by treating the nest
with a labeled
insecticide.
Even when
insecticides are
used, it is a
good idea to
remove the nest
to prevent other
insects from
being attracted
Mud dauber (Chalybion californicum) on next.
(Photo – Garland McIlveen) to it.
(Photo – Mike E. Merchant)
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Tips for Professionals
Because of the hazards and difficulty applying
insecticides to some nest sites, wasp control is usually
best left for professionals. In difficult wasp control situations, pest management professionals should
observe the following tips:
■ Provide protective coveralls and bee veils to all
workers attempting control of bees, hornets and
yellowjackets. These articles can be purchased
through beekeeper supply houses or over the
Internet. Employees with a known history of
allergic reactions to bee stings should not undertake such jobs.
■ Under no circumstances should employees climb
ladders during control efforts without protective
gear and prior experience with stinging insects.
■ The most effective delivery systems for difficultto-reach yellowjacket or bee nests include
aerosol generators and pump-type or power
dusters. Effective insecticidal dusts include
deltamethrin and cyfluthrin. Addition of silica
gel dusts (e.g., Drione®) may enhance nest penetration and, hence, the speed of control.
Effective ULV aerosol insecticides include synergized pyrethrins and pyrethroid insecticides such
as resmethrin.
■
Portable foam generating machines can be used
to treat underground voids and voids in walls.
Foams assist in ensuring that voids are completely and uniformly treated. Be sure to follow foam
and insecticide label directions carefully to avoid
causing electrical shorts in walls.
■
■
■
Entrances to yellowjacket nests in structure
walls generally should not be sealed until the
colony has been eliminated. If nests are not completely eliminated, wasps may force their way
into homes, looking for a new point of exit from
the nest.
In addition to conventional residual insecticides,
paper wasp and other exposed wasp nests can be
treated safely with pressurized sprays of insecticide soaps, peppermint oil, eugenol and other
natural insecticides. These insecticides most
commonly work as contact killing agents only,
so re-treatment may be needed. Peppermint and
other plant-derived oils may be considered as
Green List products for purposes of use on Texas
public school grounds. For the latest in information on products approved for use in Texas
schools, visit the website at
http://schoolipm.tamu.edu or call toll free
877-747-6872. Additional information is also
available at http://insects.tamu.edu.
Control of bees is more complicated than wasp
control and generally requires nest removal.
For more information about control of honey
bee nests in and around homes, see Extension
publication L-1791, available online at
http://tcebookstore.org.
Insecticide label clearances are subject to change
and changes may have occurred since this publication was printed. The pesticide user is always
responsible for the effects of pesticides on his own
property, as well as problems caused by drift from
his property to that of others.
ALWAYS READ AND FOLLOW CAREFULLY THE
INSTRUCTIONS ON THE PESTICIDE LABEL